You’ll need to look at how you registered for UK VAT, if you registered as ‘Supplies of Digital Services (below UK VAT threshold) under VAT MOSS arrangements” then so long as you are under the UK threshold you can submit nil returns in the UK.
If you didn’t register in the UK just so you could use MOSS then you’ll need to account to HMRC for the VAT on your UK sales each quarter.
Digital services supplied to consumers or businesses outside the EU are outside the scope of EU VAT adn so wouldn’t need reporting on either MOSS or UK returns.
However you do need to be certain what is meant by digital services, as anything not in that definition may well be taxable UK sales.
I’d familiarise myself with the guidacne here: https://www.gov.uk/guidance/register-and-use-the-vat-mini-one-stop-shop and linked from there.
And as I said before as you seem uncertain as to what you’ve registered for, why you’ve registered, and what it covers, and you’re dealing with dozens of different tax regimes (do you know if you need to register in the US or South Africa etc. etc. if you’re making worldwide sales) then I really do think you need to sit down for a chat with an accountant who’s familiar with these issues as getting it wrong could be quite costly.